Heretofore, structural members of a machine tool, i.e. the machine proper and parts thereof such as a column, frames and bed, have been composed of a metal such as cast iron. While the metallic structural composition processes many favorable properties such as rigidity, wear resistance, capability of localized heat-treatment, machinability and ease of assembling as generally desired for machine structural members, it presents a variety of disadvantages and inconveniences as well. Thus, a dimensional change is thermally caused in a metallic machine tool structure in the machining process and may produce a critical effect on the machining precision and require thermal insulation and other complicated countermeasures which add to the cost of the machine tool. Further, these members naturally tend to rust and also are poor in vibration absorptivity and require electrical insulation.